Since the invention of magnetic resonance imaging (MRI), a parallel technology of injectable chemicals called contrast agents has developed. Contrast agents play an important role in the practice of medicine in that they help produce more useful MRI images for diagnostic purposes. In particular, two classes of imaging agents have been developed and adopted in clinical practice. These are: low molecular weight gadolinium complexes such as Magnavist®; and colloidal iron oxides such as Feridex I.V.® and Combidex®. Neither of these two types of agents is ideal. Problems encountered with these agents are shown in Table 1, and include: expense of components; inefficiency of synthesis; loss of coating during terminal sterilization (autoclaving); narrow range of organ uptake for purposes of imaging; toxic side-effects; restriction of use to either first pass or equilibrium dosing, and others that are described herein. Agents that overcome these problems, and that combine the properties of these two types of contrast agents, are highly desirable.
TABLE 1Comparison of ideal properties of MRI contrast agents with properties oflow molecular weight gadolinium based contrast agents and colloidal ironoxides.Properties of an ideallow molecular weightcolloidal ironcontrast agentgadoliniumoxidesLow production costs:YesNoefficient synthesisAutoclavable withoutYesNoexcipientsT1 agentYesSometimesT2 agentNoYesNon toxicYesNoImaging vascularNoNocompartment at early phase(as a bolus administration)and at a late stage(equilibrium phase)Multiple administration inNoNosingle examinationImage of multiple targetYesSometimesorgansBolus injectionYesNoLow volume of injectionNoNoIron source for anemiaNoYes